What is the relationship between tense and time? How many tenses

What is the relationship between tense and time? How many tenses do English verbs have and what are they?
【正确答案】:Tense and time are related to each other but they are not the same thing. Time is a concept and tense is a grammatical device. English verbs have two tenses: present tense and past tense. 
【题目解析】:参考教材P114